Prostaglandins play a major role in the inflammation process and the inhibition of prostaglandin production, especially production of PGG2, PGH2 and PGE2, has been a common target of antiinflammatory drug discovery. However, common non-steroidal antiinflammatory drugs (NSAIDs) that are active in reducing the prostaglandin-induced pain and swelling associated with the inflammation process are also active in affecting other prostaglandin-regulated processes not associated with the inflammation process. Thus, use of high doses of most common NSAIDs can produce severe side effects, including life threatening ulcers, which limit their therapeutic potential. An alternative to NSAIDs is the use of corticosteroids, which have even more drastic side effects, especially when long term therapy is involved.
NSAIDs prevent the production of prostaglandins by inhibiting enzymes in the human arachidonic acid/prostaglandin pathway, including the enzyme cyclooxygenase (COX). The expression of cyclooxygenase-2 (COX-2) is specifically induced in the pathological conditions such as inflammation, pain, and cancer, and is involved in the generation and maintenance of these conditions. According to the line, a series of drugs called coxibs such as celecoxib, rofecoxib, valdecoxib, parecoxib, and etoricoxib have been developed.
Compound A is disclosed in the patent literature 1, and selectively inhibits cyclooxygenase-2 over cyclooxygenase-1. Compound A affords more potent analgesia, than ibuprofen which is the first choice among the conventional drugs. Furthermore it has been confirmed in the preclinical studies that Compound A has lower renal problem which are a matter of concern in conventional COX-2 inhibitors and NSAIDs.
Coxib-drugs are useful for the treatment of diseases mediated by cyclooxygenase-2, such as inflammation, pain, cancer, fever, osteoarthritis, rheumatoid arthritis, migraine, neurodegenerative diseases, cardiovascular disease, osteoporosis, asthma, lupus and psoriasis, dysmenorrhea, premature labor, glaucoma, gout, ankylosing spondylitis, bursitis, heat burn, sprain, and contusion.
In general, active ingredients involved in coxib-drugs have a sulfonamide group, whereas Compound A is a unique chemical structure, which has neither sulfonamide group nor alkylsulfonyl group but has a carboxylic acid group. Hereafter in the present specification, such coxib-drugs or coxib-compounds, which have neither a sulfonamide group nor an alkylsulfonyl group but have a carboxylic acid group, are called third generation coxib-drugs or third generation coxib-compounds. As Compound A has a carboxylic acid group in its chemical structure, the solubility in the low pH field is inferior to that in the neutral or basic condition. Therefore, depending on gastric residence time, the solubility problem may cause the precipitation of the compound followed by insufficient absorption, resulting in decreasing blood concentration and bioavailability. These adverse events are observed in common with third generation coxib-drugs or third generation coxib-compounds defined in the present specification.
Actually, results of clinical studies are obtained that when Compound A through the present specification, was administered with the standard tablet formulation, the initial blood concentration after the administration was low comparing with administered with the solution (OPC, Oral Powder Constitution: a solution in which the active ingredient is simply dissolved).
From this background, it has been investigated that a method for providing a pharmaceutical composition of a cyclooxygenase-2 inhibitor in which the stability and/or solubility are improved. Namely, the patent literature 2 discloses “a novel injectable pharmaceutical composition comprising at least one COX-2 inhibitor or NSAID or COX/LOX inhibitor or its tautomeric forms, or its analogues, isomers, polymorphs, solvates, prodrugs, or salts or thereof as active ingredient from 0.1% to 80% w/v and a solvent system comprising a mixture of glycols from 1% to 80% v/v; optionally with other pharmaceutically acceptable excipients” and also discloses “a composition according to claim 1, wherein the said composition additionally comprises at least one alkalizing agent from 0.2% to 60% v/v”. However, this is a pharmaceutical formulation as an injectable drug, and therefore an effectual means as an oral formulation which solves these issues has been desired. In addition, other technologies for solving such issues have also been desired.
As a method for keeping the basicity of the third generation coxib-drugs, a method of adding a base such as calcium carbonate, calcium hydroxide, magnesium carbonate, magnesium silicate, and magnesium aluminate as an excipient was tried, but when adding such a basic alkaline-earth metal salt to Compound A, no preferable results were obtained.